In diesel engines containing valve seat inserts, more restrictive exhaust emissions laws for diesel engines have driven changes in engine design including the need for high-pressure electronic fuel injection systems. Engines built with these systems have experienced significantly higher wear rates in their intake inserts and valves. This has driven a shift in material selection toward materials which offer improved wear resistance relative to the martensitic stainless steels which have traditionally been employed by the diesel industry.
Another emerging trend in diesel engine development is the use of EGR (exhaust gas recirculation) to further reduce exhaust emissions. With EGR, exhaust gas is routed back into the intake air stream. Since exhaust gas contains compounds of nitrogen, sulfur, chlorine, and other elements which potentially can form acids, the need for improved corrosion resistance for alloys used in intake insert applications is greatly increased for diesel engines using EGR. Acid can attack both insert and valves leading to premature engine failure. Earlier attempts to achieve improved corrosion resistance were typically accomplished through the use of martensitic stainless steels. Though these steels provide good corrosion resistance, martensitic stainless steels do not have adequate wear resistance to meet the requirements for valve seat inserts in modem diesel truck engines.
A desirable alloy would exhibit good corrosion and wear resistance suitable for use in intake insert applications in diesel engines using EGR.